Those values are set by some component, most likely a layout group on the parent. At the top of the rect transform component there should be a message like “Some values driven by …” that tells you which component is locking them.
In case of a layout group, you might want to uncheck “Control Child Size”, which will let you to resize the children freely. Or you can add a LayoutElement component on the children to set their min/max/preferred size to have a more responsive layout.
It said “Some values drivem by Canvas” and when I checked it my canvas looks lik this
Render mode: screen space - overlay
Pixel perfect:
Target display: display 1
Additional shader Ch: mixed
Vertex color always:
What should I change there?
Unless it’s a world-space canvas, the canvas size will match the camera it’s rendering for and you shouldn’t need to adjust it. If you want to set how its contents are scaled, then you need to adjust (or add) the canvas scaler component.